The limit is one order of magnitude higher than that set in the
previous experiment [1]}. Theoretical calculations
for the \(2\nu 2\beta ^-\)  decay of \(^{198}\) Pt to the ground state of
the daughter are in the interval \(T_{1/2}\sim 5\times 10^{21}-5\times 10^{23}\)  yr [2]}, [3]}. Similar
estimations give semiempirical formulae: \(T_{1/2}=(3.0\pm 1.5)\times 10^{23}\)  yr [4]} and \(T_{1/2}=3.3\times 10^{22}\)  yr [5]}. A probability of the
\(2\nu 2\beta ^-\)  decay to the \(2^+\)  411.8 keV excited level is
expected to be several orders of magnitude lower due to a smaller
value of the phase space factor and the spin change. The
theoretical estimations of the \(0\nu 2\beta ^-\)  decay of \(^{198}\) Pt
to the ground state of \(^{198}\) Hg are much higher: \(T_{1/2}\sim 3\times 10^{26}-2\times 10^{28}\)  yr
[2]}, [7]}, [8]}, [9]}The calculations were
performed for the effective Majorana neutrino mass \(\langle m_{\nu }\rangle =0.1\)  eV and \(g_A\approx 1.27\) ., while the
\(0\nu 2\beta ^-\)  transition to the \(2^+\)  411.8 keV excited level of
\(^{198}\) Hg is expected to be further suppressed. Thus, the
sensitivity of the present experiment is rather far from the
theoretical predictions for the two-neutrino mode of the decay,
not to say for the neutrinoless process.
